The present invention generally relates to an ink-jet recording device, and particularly, to an electrostatic inkjet recording device in which a recording is achieved by controlling coloring particles in a pigmentary ink through the electrophoretic effect and discharging a jet of coloring particles by means of electrostatic force.
An example of such a recording device is shown in FIG. 1. In FIG. 1, the ink-jet recording device comprises an ink chamber 201 filled with pigmentary ink, an electrophoretic electrode 203 for gathering the coloring particle 206 or charged toner around an ink discharge aperture 202 by means of the electrophoretic effect, and a discharge electrode 205 for discharging a jet of charged toner gathered around the ink discharge aperture toward a recording medium 204 to record on.
The ink chamber 201 is provided within a dielectric member 208. The ink discharge aperture 202 is provided in the dielectric member 208 for communicating the inside and the out side of the ink chamber 201. The discharge electrode 205 has a long and narrow form disposed in the ink discharging direction, and has its end pointed like a needle so as to facilitate electric field concentration on the end. The electrophoretic electrode 203 is fixed as one body on the side and back surfaces of the dielectric member 208. A grounded facing electrode 214 is provided counter the ink discharge aperture 202 via the recording medium 204. The pigmentary ink comprises petroleum organic solvent (isoparaffin) and coloring particles 206 of thermoplastic resin colored with electrification control agent or toner dispersed in the organic solvent. The toner is charged apparently positive by the zeta potential. The recording object 204 is ordinary paper. The electrophoretic electrode 203 and the discharge electrode 205 are connected to a voltage driver (not shown) for applying predetermined voltages with a polarity opposite from that of the coloring particle 206 to the electrodes 203 and 205 in predetermined timing.
FIG. 2 is a diagram showing the voltages applied to the electrophoretic electrode 203 and the discharge electrode 205 in printing operation of the recording device of FIG. 1. In FIG. 2, if a constant voltage V1 is applied to the electrophoretic electrode 203 as shown in FIG. 2A, forming an electric field in the ink chamber 201 filled with pigmentary ink, then the coloring particles 206 in the pigmentary ink moves at an electrophoretic speed toward the ink discharge aperture 202 by the action of the electric field, and eventually gathers around the ink discharge aperture 202. If a pulse voltage V2 with a duration of T2 is applied to the discharge electrode 205 with the coloring particles 206 gathered around the ink discharge aperture, then a jet of coloring ink is discharged in synchronism with the pulse voltage V2 from the ink discharge aperture 202 in the form of a flying particle group 207, which adheres to the recording medium 204. Subsequently, the electric field formed by the electrophoretic electrode 203 causes coloring particles 206 to be supplied to the ink discharge aperture 202. Thus, the discharge of coloring particle is repeated, resulting in a formation of image on the recording medium 204.
However, in the conventional ink-jet recording device as described above, the coloring particles 206 keep moving toward the ink discharge aperture 202 as long as the constant voltage VI shown in FIG. 2 is applied to the electrophoretic electrode 203. If no coloring particle 206 has been discharged from the ink discharge aperture 202 for a long time, then too many coloring particles will gathering around the ink discharge aperture 202, causing an obstruction in the ink discharge aperture 202. This prevents stable discharging of coloring particles 202, having adverse influence on the quality of printed images.
The above and other problems in the prior art are solved and advances are made by the present invention. It is an object of the invention to provide an electrostatic ink-jet recording device for providing a stable printing by preventing too many coloring particles from gathering around the ink discharge aperture.